Implantable generator having current steering means

ABSTRACT

An implantable pulse generator includes a current steering capability that allows a clinician or patient to quickly determine a desired electrode stimulation pattern, including which electrodes of a group of electrodes within an electrode array should receive a stimulation current, including the amplitude, width and pulse repetition rate of such current. Movement of the selected group of electrodes is facilitated through the use of remotely generated directional signals, generated by a pointing device, such as a joystick. As movement of the selected group of electrodes occurs, current redistribution amongst the various electrode contacts takes place. The redistribution of stimulus amplitudes utilizes re-normalization of amplitudes so that the perceptual level remains fairly constant. This prevents the resulting paresthesia from falling below the perceptual threshold or above the comfort threshold.

This application is a continuation of U.S. application Ser. No.10/150,879 filed May 17, 2002, now U.S. Pat. No. 6,609,032; whichapplication is a continuation of Ser. No. 09/550,217, filed Apr. 17,2000, now U.S. Pat. No. 6,393,325; which application is acontinuation-in-part of U.S. patent application Ser. No. 09/226,849,filed Jan. 7, 1999, now U.S. Pat. No. 6,052,624; which applicationclaims the benefit of the following U.S. Provisional Applications: Ser.No. 60/145,829, filed Jul. 27, 1999, and Ser. No. 60/172,167, filed Dec.17, 1999; which applications and patents are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a device for programming an implantableelectrode array used with an implantable stimulator. More particularly,one embodiment of the invention relates to a device used to providedirectional programming for the implantable electrode array associatedwith an implantable stimulator that electrically stimulates the spinalcord for the purposes of controlling and reducing pain.

Within the past several years, rapid advances have been made in medicaldevices and apparatus for controlling chronic intractable pain. One suchapparatus involves the implantation of an electrode array within thebody to electrically stimulate the area of the spinal cord that conductselectrochemical signals to and from the pain site. The stimulationcreates the sensation known as paresthesia, which can be characterizedas an alternative sensation that replaces the pain signals sensed by thepatient. One theory of the mechanism of action of electrical stimulationof the spinal cord for pain relief is the “gate control theory”. Thistheory suggests that by simulating cells wherein the cell activitycounters the conduction of the pain signal along the path to the brain,the pain signal can be blocked from passage.

Spinal cord stimulator and other implantable tissue stimulator systemscome in two general types: “RF” controlled and fully implanted. The typecommonly referred to as an “RF” system includes an external transmitterinductively coupled via an electromagnetic link to an implanted receiverthat is connected to a lead with one or more electrodes for stimulatingthe tissue. The power source, e.g., a battery, for powering theimplanted receiver-stimulator as well as the control circuitry tocommand the implant is maintained in the external unit, a hand-heldsized device that is typically worn on the patient's belt or carried ina pocket. The data/power signals are transcutaneously coupled from acable-connected transmission coil placed over the implantedreceiver-stimulator device. The implanted receiver-stimulator devicereceives the signal and generates the stimulation. The external deviceusually has some patient control over selected stimulating parameters,and can be programmed from a physician programming system. An example ofan RF system is described, e.g., in U.S. Pat. No. 4,793,353,incorporated herein by reference.

The fully implanted type of stimulating system contains the programmablestimulation information in memory, as well as a power supply, e.g., abattery, all within the implanted pulse generator, or “implant”, so thatonce programmed and turned on, the implant can operate independently ofexternal hardware. The implant is turned on end off and programmed togenerate the desired stimulation pulses from an external programmingdevice using transcutaneous electromagnetic, or RF links. Suchstimulation parameters include, e.g., the pulse width, pulse amplitude,repetition rate, and burst rates. An example of such acommercially-available implantable device is the Medtronic Itrel II,Model 7424. Such device is substantially described in U.S. Pat. No.4,520,825, also incorporated herein by reference.

The '825 patent describes a circuit implementation of a cyclic gradualturn on, or ramping of the output amplitude, of a programmable tissuestimulator. The implementation contains separate memory cells forprogramming the output amplitude and number of pulses at each increasingoutput level or “step”. In devices of the type described in thereferenced '825 patent, it is desirable to provide some means of controlover the amplitude (intensity), the frequency, and the width of thestimulating pulses. Such control affords the patient using the devicethe ability to adjust the device for maximum effectiveness. For example,if the pulse amplitude is set too low, there may be insufficient painrelief for the user; yet, if the pulse amplitude is set too high, theremay be an unpleasant or uncomfortable stinging or tingling sensationfelt by the user. Moreover, the optimum stimulation parameters maychange over time. That is, numerous and varied factors may influence theoptimum stimulation parameters, such as the length of time thestimulation has been ON, user (patient) postural changes, user activity,medicines or drugs taken by the user, or the like.

In more complex stimulation systems, one or more leads can be attachedto the pulse generator, with each lead usually having multiple electrodecontacts, Each electrode contact can be programmed to assume a positive(anode), negative (cathode), or OFF polarity to create a particularstimulation field when current is applied. Thus, different combinationsof programmed anode and cathode electrode contacts can be used todeliver a variety of current waveforms to stimulate the tissuesurrounding the electrode contacts.

Within such complex systems, once one or more electrode arrays areimplanted in the spinal cord, the ability to create paresthesia over thepainful site is firstly dependent upon the ability to accurately locatethe stimulation site. This may more readily be accomplished byprogramming the selection of electrode contacts within the array(s) thanby physically maneuvering the lead (and hence physically relocating theelectrode contacts). Thus, the electrode arrays may be implanted in thevicinity of the target site, and then the individual electrode contactswithin the array(s) are selected to identify an electrode contactcombination that best addresses the painful site. In other words,electrode programming may be used to pinpoint the stimulation areacorrelating to the pain. Such electrode programming ability isparticularly advantageous after implant should the lead contactsgradually or unexpectedly move, thereby relocating the paresthesia awayfrom the pain site. With electrode programmability, the stimulation areacan often be moved back to the effective site without having tore-operate on the patient in order to reposition the lead and itselectrode array.

Electrode programming has provided different clinical results usingdifferent combinations of electrode contacts and stimulation parameters,such as pulse width, amplitude and frequency. Hence, an effective spinalcord stimulation system should provide flexible programming to allowcustomization of the stimulation profile for the patient, and therebyallow for easy changes to such stimulation profile over time, as needed.

The physician generally programs the implant, external controller,and/or external patient programmer through a computerized programmingstation or programming system. This programming system can be aself-contained hardware/software system, or can be defined predominatelyby software running on a standard personal computer (PC). The PC orcustom hardware can have a transmitting coil attachment to allow for theprogramming of implants, or other attachments to program external units.Patients are generally provided hand-held programmers that are morelimited in scope than are the physician-programming systems, with suchhand-held programmers still providing the patient with some control overselected parameters.

Programming of the pulse generators, or implants, can be divided intotwo main programming categories: (1) programming of stimulation pulsevariables, and (2) programming electrode configurations. Programmablestimulation pulse variables, as previously indicated, typically includepulse amplitude, pulse duration, pulse repetition rate, burst rate, andthe like. Programmable electrode configuration includes the selection ofelectrodes for simulation from the available electrode contacts withinthe array as well as electrode polarity (+/−) assignments. Factors toconsider when programming an electrode configuration include the numberof electrode contacts to be selected, the polarity assigned to eachselected electrode contact, and the location of each selected electrodecontact within the array relative to the spinal cord, and the distancebetween selected electrodes (anodes and cathodes), all of which factorscombine to define a stimulation field. The clinician's electrodeselection results in a simulating “group” containing at least one anodeand at least one cathode that can be used to pass stimulating currentsdefined by the programmed pulse variables. For an electrode array havingeight electrode contacts, this can result in an unreasonable largenumber of possible combinations, or stimulation groups, to chose from.

Moreover, within each stimulation group, there are a large number ofpulse stimulation parameters that may be selected. Thus, through theprogrammer, the clinician must select each electrode, includingpolarity, for stimulation to create each combination of electrodecontacts for patient testing. Then, for each combination, the clinicianadjusts the stimulation parameters for patient feedback until theoptimal pain relief is found for the patient. Disadvantageously, it isdifficult to test many stimulation variables with hundreds or eventhousands of possible electrode and stimulus parameter combinations. Totest all such combinations, which is typically necessary in order tofind the optimum stimulation settings, is a very lengthy and tediousprocess. Because an all-combination test is lengthy and tedious, someclinicians may not bother to test many different electrode combinations,including many that may be considered far more optimal than what isultimately programmed for the patient. It is thus evident that there isa need in the art for a more manageable programming technique fortesting and handling a large number of possible electrode and pulseparameter combinations.

One method that has recently been developed for simplifying theprogramming process is described in U.S. Pat. No. 5,370,672,incorporated herein by reference. The '672 patent describes aprogramming system where the patient interacts with the clinician'sprogrammer. More specifically, the '672 patent teaches a system whereinthe patient identifies the pain site by “drawing” the pain site on atouch screen that displays an illustration of the human body. Afterentering the patient's stimulation thresholds and associated tolerancesinto the system, the computer generates a recommended electrodeconfiguration for that patient using algorithms based on spinal cordstimulation research. The patient responds to the resulting stimulationby drawing the amount of paresthesia coverage over the bodyillustration. If the drawing paresthesia site does not fully match thepain site, the system adjusts the recommendation, and the patientresponds again to the new sense of paresthesia. This process is repeateduntil the best-tested settings are reached.

Advantageously, the process described in the '672 patent effectivelyeliminates the manual selection of electrode combinations, and reducesthe selection process to a reasonable testing of electrode/parametercombinations based on an extensive pre-organized set of rules forprogramming optimization and patient input. Moreover, thephysician/clinician is not directly controlling the programming session;rather, the patient provides the system with the feedback without theneed for the physician or clinician to interpret the patient'ssensations or empirically estimate changes required in stimulationparameters.

Disadvantageously, using the method described in the '672 patent, thepatient must still test and respond to each of the chosen combinationsand must depend upon the system recommendations, which systemrecommendations might exclude a possible optimal setting for thatpatient. Further, the patient must be able to accurately translatesubtle sensations and differences to a drawing on a screen, and thenwait for device programming before having to react and redraw theparesthesia from the new settings. Such process can still be timeconsuming. Furthermore, subtle sensation differences felt by the patientbetween combinations cannot necessarily be translated in a drawing ofparesthesia that only address “coverage area.” In summary, by reducingthe combinations to a computer-generated recommendation, many electrodecombinations might be omitted that could provide a more effectiveparesthesia. Hence, the process of computer-recommended combinations,although superior to manual arbitrary selection, can still be viewed asan undesirable “discrete” method of patient feedback evaluation: i.e.,electrodes are programmed and patient feedback is entered for eachcombination, one iteration at a time.

In view of the above, it is evident that profound improvements are stillneeded in the way multiple implanted electrode combinations areprogrammed. In particular, it is seen that improvements in programmingtechniques and methods are needed that do not compromise the patient'sability to feel the subtle effects of many different combinations, andthat provide a more immediately responsive programming-to-feedback loop.

SUMMARY OF THE INVENTION

The present invention advantageously addresses the needs above, as wellas other needs, by providing improved programming methods for electrodearrays having a multiplicity of electrodes. The present inventionadvantageously simplifies the programming of multiple electrode contactconfigurations by using a directional input device in conjunction with aprogrammer/controller to automatically combine and reconfigureelectrodes with alternating current paths as determined by thedirectional input device. The directional input device used with theinvention may take many forms, e.g., a joystick, a button pad, a groupof keyboard arrow keys, a touch screen, a mouse, or equivalentdirectional input mechanisms. Advantageously, the use of a directionalinput device to automatically adjust electrode configurations in orderto “steer” the stimulation current allows the patient to immediatelyfeel the effect of electrode configuration changes. Then, without havingto translate the subtle differences of sensation to a drawing fordiscrete computer-generated recommendations, or manually and arbitrarilyselecting different combinations, the patient responds continuously tothe sensation by steering directional or equivalent controls. Hence, thepatient more directly controls the programming without being cognizantof actual electrode combinations and variables. The patient is also moreimmediately responsive, since there is no need to translate theperceived sensations to specific locations on a displayed drawing. Thisprocess is thus analogous to continuous feedback as opposed to discretefeedback and system manipulation.

While the directional programming device provided by the invention isprimarily intended to program implanted stimulator devices having atleast two electrode contacts, it should also be noted that it can alsobe used to program the electrodes used with external stimulators.

The invention described herein thus relates, inter alia, to a method ofprogramming utilizing directional input signals to “steer” and definecurrent fields through responsive automated electrode configuring.Hence, in accordance with one aspect of the invention, programmingequipment is utilized including a computer and/or custom transmitter,coil and programming software to achieve the desired current fieldsteering effect. Additional control mechanisms (software and/orhardware) are used to respond to directional control signals generated,e.g., with a joystick or other directional means, so as to configure andcombine the electrodes as directed by the joystick or otherdirectional-setting device so as to redistribute the current/voltagefield in a way that prevents the paresthesia felt by the patient fromeither falling below a perceptual threshold or rising above a comfortthreshold. As needed, one or more other input devices can be used tocontrol different aspects of the electrode configuration.

In accordance with another aspect of the invention, a representation ofthe changing current fields resulting from movement of the directionaldevice is visually provided on a display screen associated with theprogramming equipment, thereby providing visual feedback to the user asto the electrode configurations and/or resulting stimulation fields thatare achieved through manipulation of the directional input mechanism.

In use, a spinal cord stimulator is implanted with one or more leadsattached to the spinal cord. The implanted spinal cord stimulator iscoupled through an RF or other suitable link to the external spinal cordstimulation system, which system is used to program and/or control theimplanted stimulator. The style and number of leads are entered into thesystem software. The clinician then maneuvers the joystick, or otherdirectional instructor, to redirect current to different groups ofimplanted electrodes. The software then automatically reconfigureselectrodes according to directional responsive rules in the softwareand/or electronics. Automatic configuring of the electrodes to steercurrent includes, e.g., the number of electrodes, the selection ofelectrodes, the polarity designation of individual electrodes, and thedistribution of stimulation intensities among the selected electrodes.

The advantage achieved with the programming system provided by theinvention is that the clinician never has to actually select and test amultitude of electrode combinations with the patient, which otherwisetakes time for each configuration. Instead, the patient immediatelyresponds to maneuvers conducted by himself/herself or the clinician,which causes the user to move toward or away from certain directions.The directional programming feature may also be made available directlyto the patient through a small portable programming device.Advantageously, all reconfiguring of the electrodes is doneautomatically as a function of the directional signals generated by thejoystick or other directional device(s), and is done in a way thatprevents the paresthesia felt by the patient from falling below theperceptual threshold or rising above the comfort threshold.

One embodiment of the invention may be viewed as a programming systemfor use with a neural stimulation system. Such neural stimulation systemincludes: (1) a multiplicity of implantable electrodes adapted tocontact body tissue to be stimulated; (2) an implantable pulse generatorconnected to each of the multiplicity of electrodes, the implantablepulse generator having electrical circuitry responsive to programmingsignals that selectively activates a plurality of the implantableelectrodes, wherein at least one electrode in the plurality of activatedimplantable electrodes functions as a cathode, and wherein at least oneelectrode in the plurality of activated implantable electrodes functionsas an anode, whereby stimulus current flows from the at least oneactivated anodic electrode to the at least one activated cathodicelectrode; (3) a programming device coupled with the implantable pulsegenerator, the programming device having control circuitry thatgenerates programming signals adapted to control the implantable pulsegenerator; (4) an input device coupled with the programming device,wherein the input device generates directional signals as a function ofuser control; and (5) control logic within the programming device thatcontinuously activates selected ones of the multiplicity of implantableelectrodes in response to the directional signals received from the usercontrolled input device, whereby stimulus current is selectivelyredistributed among cathodic and anodic electrodes as directed by theuser controlled input device. The electrical circuitry within theimplantable pulse generator may activate the selected electrodes byforcing a prescribed current to flow into (a current sink) a cathodicelectrode, by forcing a prescribed current to flow from (a currentsource) an anodic electrode, by causing a prescribed positive voltage tobe applied to an anodic electrode, by causing a prescribed negativevoltage to be applied to a cathodic electrode, or by combinations of theabove.

It is thus a feature of the present invention to provide a system and amethod for programming that allows a clinician or patient to quicklydetermine a desired electrode stimulation pattern, including whichelectrodes of a multiplicity of electrodes in an electrode array shouldreceive a stimulation current, the polarity, distance between anodes andcathodes, and distribution of stimulation intensity or amplitude.

It is another feature of the invention to provide an electrode selectionsystem that allows the user (the person operating the programmer) toreadily select and visualize a particular group of electrodes of anelectrode array for receipt of a stimulation pulse current, and whenselected to allow different combinations of pulse amplitude, pulsewidth, pulse repetition rate, or other pulse-defining parameters to beapplied to the selected group.

It is yet an additional feature of the invention to allow an implantabletissue stimulator, having an array of stimulation electrodes attachedthereto, to be readily and quickly programmed so that only thoseelectrodes which prove most effective for a desired purpose, e.g., painrelief, are selected and configured to receive a pulsed current havingan amplitude, width, repetition frequency, or burst parameters that bestmeets the needs of a particular patient.

It is still another feature of the invention to provide a system and amethod of steering or programming the perceived paresthesia so that anyneeded redistribution of the stimulus current occurs in small stepsizes, thereby making neural recruitment more effective. In accordancewith this feature of the invention, the small step size in current orvoltage amplitude settings that is used amongst the electrode contactsis selected to effectively correspond to the spatial resolution to whichneural elements can be activated. That is, this spatial resolution ismeaningful to the extent that the micro-anatomy of the neural structuresbeing activated gives rise to different clinical effects.Advantageously, by using such a system that automatically redistributescurrent or voltage amplitudes amongst electrodes in suitable small stepsizes, desired neural activation patterns may be found more easily.

It is another feature of the invention to provide a system forredistributing current and/or voltage amplitudes amongst selectedelectrodes using a user interface that is simple and intuitive.

It is an object of the invention to eliminate the need for either aclinician to manually select electrode combinations, or even for acomputer to select electrode combinations that must be discretely testedfor patient feedback. That is, based on the feedback as to the amount ofcoverage, an educated guess for another combination must be made (byclinician or computer) and the patient must then discretely respond tothat combination before another combination is set up and turned on.Such discrete testing with patient feedback is very tedious and timeconsuming. Advantageously, by practicing the present invention, discreteselection and patient feedback of location and amount of paresthesiacoverage (either to the clinician or to a computer) is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will be more apparent from the following more particulardescription thereof, presented in conjunction with the followingdrawings wherein:

FIG. 1A is a perspective view of one embodiment of a directionalprogrammer device with a visual display in accordance with the presentinvention;

FIG. 1B is a perspective view of another embodiment of a directionalprogrammer device in accordance with the present invention;

FIG. 2 is a functional block diagram of a directional programmer systemin accordance with the present invention;

FIG. 3 is a schematic view of a patient with an implanted stimulator,coupled to a directional programmer system;

FIG. 4 is a view of the directional programmer display screen of FIG.1A;

FIG. 5A schematically illustrates the various functions provided by thedirectional-programmer device;

FIG. 5B illustrates one type of electrode grouping that may be achievedwith the invention;

FIG. 6A illustrates a representative electrode array usable with theinvention having eight electrode contacts;

FIG. 6B illustrates an alternative electrode array usable with theinvention;

FIG. 6C illustrates yet another representative electrode array usablewith the invention;

FIG. 7 shows a table-based current shifting algorithm for horizontalshifting;

FIGS. 8 and 8A-8Q (note, there is no FIG. 8I or FIG. 8O) show atable-based current shifting algorithm for vertical shifting, with FIG.8 providing a map to FIGS. 8A-8Q;

FIG. 9 is a block diagram of the software architecture used in an SCSsystem, or other neural stimulation system, in accordance with thepresent invention;

FIG. 10 depicts a representative patent information screen that may beused with the software architecture of FIG. 9;

FIG. 11 is a flow chart that depicts the steps utilized by a softwarewizard in order to guide a user through the fitting process associatedwith an SCS, or other neural stimulation system;

FIGS. 12A through 12J (note, there is no FIG. 12I) illustrate variousscreens that may be used by the software wizard as it carries out thesteps depicted in FIG. 11;

FIG. 13 illustrates a representative measurement screen used as a partof the fitting process which graphically shows the measured andcalculated threshold settings;

FIG. 14 illustrates a representative programming screen used as part ofthe fitting process carried out by the software wizard of FIG. 11;

FIG. 15 similarly illustrates a representative programming screen usedas part of the fitting process; and

FIG. 16 shows an illustrative navigator map that may be used with thefitting system of the present invention in order to teach and guide thepatient through the complete fitting process.

Like reference numerals are used to refer to like elements or componentsthroughout the several drawing figures.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

At the outset, it is to be noted that a preferred implementation for adirectional programming device in accordance with the present inventionis through the use of a joystick-type device or equivalent. Hence, inthe description that follows, a joystick device is described. It is tobe understood, however, that other directional-programming devices mayalso be used in lieu of a joystick, e.g., a roller ball tracking device,horizontal and vertical rocker-type arm switches, selected keys (e.g.,directional-arrow keys) on a computer keyboard, touch-sensitive surfaceson which a thumb or finger may be placed, recognized voice commands(e.g., “up”, “down”, “diagonal”, etc.), recognized movement of bodyparts (e.g., detecting eye blinks, finger taping, muscle contraction,etc.), and the like. Any type of hardware or software that allowsdirectional signals to be generated through motion or movement of a bodypart, or through the movement of keys, levers, or the like, or throughrecognition of voice or visual commands, may be used as the directionalprogramming device used with the invention.

Thus, it is seen that any input device capable of driving software,electrical hardware, as well as mechanical systems that configurestimulation electrodes, may be used with the present invention as adirectional programming device. Additional input devices include voiceactivated and mechanical dials that can cause the switching ofelectrodes and output distributions. The shifting of electrodes occursin response to input signals derived from the user controlled inputdevice.

While the embodiment described below relates to a spinal cord stimulatorfor the treatment of pain, it is to be understood that the principles ofthe invention also apply to other types of tissue stimulator systems.Likewise, although the preferred embodiment includes software for use inconjunction with a PC, it is to be understood that the invention canalso be implemented through custom programming devices for either theclinician or the patient, with or without visual displays.

Turning first to FIG. 1A, there is shown a representative view of adirectional programmer system 10 implemented in accordance with oneembodiment of the invention. Such system 10 comprises a joystick 12 (orother type of directional programming device), a keyboard 14, and aprogramming display screen 16, housed in a case 18. As seen in FIG. 1A,the overall appearance of the system 10 is that of a laptop personalcomputer (PC) and, in fact, the system 10 may be implemented using a PCthat has been appropriately configured to include adirectional-programming device and programmed to perform the functionsdescribed herein. As indicated previously, it is to be understood thatin addition to, or in lieu of, the joystick 12, other directionalprogramming devices may be used, such as a mouse 13, or directional keys15 included as part of the keys associated with the keyboard 14.

FIG. 1B depicts a custom directional programmer system 10′ that may alsobe used with the invention. The programmer system 10′ is built within acase 18′ designed to fit within the hand of the user, and includes anarray 12′ of directional keys which allow directional signals to begenerated, equivalent to those generated by a joystick. The hand-heldunit 10′ further includes a functional display 16′, typically realizedusing light emitting diodes (LEDs), as is known in the art. Variousprogrammable features or functions associated with the programmer system10′ may be selected using the keys 17′. Once selected, a “store” button19′ is provided to allow a desired electrode configuration, includingother selected parameters, or a desired function, to be selected andsaved in memory so that it can be recalled as desired to define theelectrode configuration to be used at a later date.

The joystick programmer system 10 of FIG. 1A, or the alternate hand-heldprogrammer 10′ of FIG. 1B, is intended to be used with an implantedtissue stimulator, e.g., an implantable spinal cord tissue stimulator 20(see FIG. 3). A spinal cord tissue stimulator, as shown in FIG. 3, istypically implanted in the abdomen of a patient 22. An electrode array23, electrically connected to the simulator 20, has individual electrodecontacts, or electrodes 24, arranged in a desired pattern and positionednear the spinal column 26, The spinal stimulator 20, when appropriatelyprogrammed, is used by the patient for the control of pain. A morethorough description of a spinal cord stimulator may be found in thepreviously referenced '829 provisional patent application, whichapplication has been incorporated herein by reference.

Advantageously, the directional programmer systems 10 or 10′ greatlysimplify the programming of multiple implanted electrode contactconfigurations. As previously indicated, programming systems currentlyrequire the physician or clinician to specifically select and manuallyinput the electrode combinations that are to used for stimulation—atime-consuming and frustrating process. In contrast, the presentinvention allows the physician or clinician to readily determine adesired combination of electrodes, i.e., a selected “group” ofelectrodes, using the joystick 12 (or other directional programmingdevice) that affects which electrodes are selected, the polarity ofindividual electrodes, and the stimulation intensity distribution, allof which parameters can contribute to “steer” and/or “focus” thestimulation current. In other words, through use of the presentinvention, the operator can adjust the stimulation field location,concentration and spread by maneuvering the joystick 12 thatautomatically configures electrodes for stimulation. Advantageously, asthe stimulating group of electrodes is being configured and positionedusing the directional signals generated by the joystick 12, theprogrammed stimulation is automatically directed to the electrodes forimmediate and continuous patient response. A preferred technique forgenerating the directional signals that are automatically directed toelectrodes in accordance with the invention, particularly in relation tomoving the directional signals from one stimulation site to another insmall steps, is described hereinafter.

FIG. 2 shows a functional block diagram of a directional programmingsystem 10 made in accordance with the present invention, and furtherincludes a functional block diagram of the implantable tissue stimulator20 that is programmed and controlled using such system. It is to beemphasized that the block diagram shown in FIG. 2 is a functional blockdiagram, i.e., a diagram that illustrates the functions performed by theprogramming system 10 and stimulator 20. Those of skill in the art,given the descriptions of the invention presented herein, can readilyconfigure various hardware and/or software components that may be usedto carry out the functions of the invention.

The implantable tissue stimulator 20 will be described first. It shouldbe noted that the implantable tissue stimulator 20, per se, is not thesubject of the present invention. Rather, the invention relates to adevice or system for programming and/or controlling the stimulator 20 sothat a desired pattern of tissue stimulation currents are applied to aselected group of electrodes that form part of the tissue stimulator 20.Nonetheless, in order to better understand and appreciate how theprogramming system 10 of the invention interacts with the stimulator 20,it will also be helpful to have at least a functional understanding ofhow the stimulator 20 operates.

Thus, as seen in FIG. 2, the implantable tissue stimulator 20 includes acoil 62 for receiving RF or other control signals and power from anexternal source, e.g., from the programmer 10. The signals thus receivedare passed through a receiver circuit 64. A rectifier/filter circuit 68extracts power from the received signals and presents such extractedpower to a voltage regulator circuit 74, which regulator circuit 74generates the operating voltages needed within the implantablestimulator device 20. A preferred implantable tissue stimulator 20includes a rechargeable or replenishable energy source 78, e.g., arechargeable battery and/or large capacitor. If so, a suitablerecharging circuit 76 derives power from the voltage regulator 74 and/orrectifier/filter circuit 68 for recharging or replenishing such powersource 78. The power source 78, in turn, provides its stored energy tothe voltage regulator circuit 74.

The signals received by the implant receiver circuit 64 are alsodirected to a data demodulator 66, which demodulator demodulates thecontrol information (data) that is included in the signals received fromthe programmer 10. Typically, such control data are arranged in asequence of frames, with certain bits of data in each frame signifyingdifferent commands or other information needed by the tissue stimulator20 in order for it to carry out its intended function. Such controldata, once recovered by the data demodulator 66, is presented to acontroller 70, e.g., a microprocessor (μP) controller. The μP controller70, upon receipt of the data, acts upon it in order to carry outwhatever commands have been received.

The μP controller 70 may be programmed to operate in numerous modes.Typically, an operating program, stored in a suitable memory device 67included within the implantable stimulator 20, directs or controls theμP controller 70 to carry out a sequence of operations. In someimplementations, the operating program itself may be received andprogrammed into the memory 67 through receipt of the data commandsreceived from the programmer 10. In other implementations, a basicoperating program is permanently stored in the memory 67, e.g, in a readonly memory (ROM) portion of memory 67, and various parametersassociated with carrying out such basic operating program may bemodified and stored in a random access memory (RAM) portion of thememory 67 through the data commands received from the programmer 10.

Regardless of how the operating program is received and stored withinthe tissue stimulator 20, it generally causes an electrical stimulationcurrent, e.g., a biphasic stimulation current, to be applied to one ormore selected pairs of a multiplicity of electrodes, E1, E2, E3, . . .En, associated with the stimulator. That is, as controlled by thecontrol signals received from the programmer 10, which signals may beacted on immediately, or stored in memory 67 for subsequent action, agiven electrode of the multiplicity of electrodes E1, E2, E3, . . . Enincluded within an array 23 of electrodes, is either turned ON or turnedOFF, and if turned ON, it receives a biphasic or other current pulsehaving a selected amplitude, pulse width, and repetition frequency. Inthis manner, then, as controlled by the control signals received fromthe programmer 10, the tissue stimulator 20 thus applies a selectedstimulation current to selected pairs of the electrodes included withinthe electrode array 23.

In some programming modes, an indifferent or return electrode, Eg, whichmay in fact form part of the case or housing of the implantablestimulator 20, may be paired with individual ones of the electrodes E1,E2, E3, . . . En so as to provide “monopolar” stimulation. When two ofthe electrodes E1, E2, E3, . . . En are paired together, suchstimulation is generally referred to as “bipolar” stimulation.Stimulation currents must always be applied through two or moreelectrodes, with at least one electrode functioning as an anode and withat least one electrode functioning as a cathode, so that the stimulationcurrent may flow into the tissue to be stimulated through one path andreturn therefrom through another path.

Still with reference to FIG. 2, the functions performed by thedirectional programmer system 10 will next be described. As seen in FIG.2, a key element of such system 10 is the directional control device 12,which may comprise, e.g., a joystick device. Coupled with thedirectional control device 12 is a plurality of up/down bottons orselector buttons 42. The control device 12 and selector buttons 42provide signals to an electrode group location/size map generatorcircuit 50 that defines a group 45 of electrodes 24 (see FIG. 4) withinthe array 23 of electrodes, which, depending upon the selected polarityof individual electrodes 24 within the group 45 of electrodes, furtherdefines an electric field 33 between the selected electrodes thateffectively defines a stimulation area 36 that receives the stimulationcurrent. The definition of the group of electrodes 45 is provided to astimulator processor circuit 52 and/or to a memory circuit 54.

Also provided to the stimulator processor circuit 52 are data thatdefine a desired pulse amplitude, pulse width, and pulse repetitionrate, and any other stimulation parameters (e.g., burst repetition rate,etc.) that characterize the stimulation pulses that are to be applied tothe selected group of electrodes. Such characterization data may bepreprogrammed into the processor 52, or it may be set through use ofmanual selection input/output (I/O) devices 35, 37 and 39, which devicesmay be implemented in hardware (e.g., slide switches) or software (e.g.,simulated slide switches that appear on the display screen 16 of theprogrammer 10). Further, amplitude programming (also referred to as“magnitude programming”), as explained in more detail below, and asfurther described in the '167 provisional patent application previouslyreferenced and incorporated herein by reference, is preferablyimplemented to facilitate the programming of the stimulator system.Other I/O devices may also be used, e.g., the keyboard 14, as required,in order to enter needed characterization data.

The stimulator processor 52 takes the pulse characterization data, aswell as the electrode group data, and processes such data so that theappropriate commands can be sent to the implantable receiver 20. Asuitable data frame format generator circuit 56 may be used to form thedata into suitable data frames that will be recognized and acted upon bythe implant stimulator 20, as is known in the art. In practice, thefunction of the data frame format generator circuit 56 may be carriedout as part of the processing functions performed by the stimulatorprocessor 52. Once properly framed, such data commands are sent to acoil driver circuit 58, which drives the external coil 28, causing suchsignals to be inductively or otherwise coupled into the implant coil 62and implant receiver circuit 64 of the implantable stimulator 20. Theimplantable stimulator 20 then acts on the data received so as toprovide the programmed stimulation currents to the group of electrodesselected by the directional device 12 and selectors 42, using thepolarity defined by the received data.

Also included as part of the programming system 10 is a display screen16, and associated screen driver circuit 15. The display screen providesa display as controlled by the stimulator processor 52 of data, or otherinformation, in conventional manner. For purposes of the presentinvention, as explained in more detail below in connection with FIGS. 4and 5A, the display screen 16 displays a simulated picture of theimplanted electrodes, as well as the selected group of electrodes. Themoving, expanding, or contracting stimulation field 33 is then displayedin response to the directional controller 12 and selection controls 42.

It is noted that the implantable stimulator 20 may also include backtelemetry capability which allows it to send data to the externalprogrammer 20. Such back telemetry data may include status signals,e.g., voltage levels within the stimulator 20, and/or sensed data, e.g.,sensed through one or more of the electrodes 24. In such instances, theprogrammer 10 includes appropriate circuitry for sensing and acting uponsuch received back telemetry data. For simplicity, such back telemetryfeatures are not included in the functional block diagram of FIG. 2, butit is to be understood that such features may be used with theinvention.

The following issued United States patents, each of which isincorporated herein by reference, provide additional detail associatedwith implantable tissue stimulators, programming such stimulators, andthe use of biphasic stimulation pulses in a bipolar, monopolar or otherstimulation mode: U.S. Pat. Nos. 5,776,172; 5,649,970; 5,626,629; and5,601,617.

Turning next to FIG. 3, a typical implanted programmable spinal cordstimulator 20 is schematically illustrated. Such stimulator is typicallyimplanted in the abdomen of a patient 22 for control of pain byelectrical stimulation of the spinal cord. The stimulator 20 isconnected to an array 23 of electrodes 24 implanted near the spinalcolumn 26 of the patient 22. The preferred placement of the electrodes24 is adjacent, i.e., resting upon, the spinal cord area to bestimulated. The stimulator 20 includes a programmable memory locatedinside of it which is used to direct electrical current to the leadelectrodes 24. Modifying the parameters in the programmable memory ofthe stimulator 20 after implantation is performed by a physician orclinician using the directional programmer system 10. For example,control signals, e.g., modulated RF signals, are transmitted to areceiving coil inside the stimulator 20 by a transmission coil 28connected to the programmer 10 via a cable 30.

In accordance with the teachings of the present invention, thedirectional programmer system 10 is used by the physician to modifyoperating parameters of the implanted electrodes 24 near the spinal cord26. As it does so, the modification of operating parameters in carriedout in an optimum manner such that changes in stimulus current occurgradually, in small steps, as the stimulus field moves from one group ofelectrodes to another. That is, in a preferred implementation, theinclusion or exclusion of a given electrode within a selected group ofelectrodes is gradually phased in or out, as directed by the directionalcontrols received from the directional programmer system 10. Theprogrammer system 10, as indicated above in connection with thedescription of FIG. 2, may selectively turn the stimulator 20 ON or OFF,or adjust other parameters such as pulse rate, pulse width and/or pulseamplitude, as desired.

FIG. 4 illustrates a representative programming display screen 16 usedwith the directional programmer system 10. The programming screen 16visually provides all of the information required to program thestimulator 20 and electrodes 24. Various types of programminginformation may be provided depending on the complexity desired from thesystem.

For the programmer system 10 to carry out its intended function, it mustknow the style, number, and location of the electrodes 24 that have beenimplanted near the spinal cord 26, along with information characterizingthe implanted spinal cord stimulator 20 (i.e., the model number whichdetermines performance capabilities of the implanted stimulator).Information regarding the type of electrode array 23, including thenumber and relative position of the individual electrodes 24 includedwithin the array 23, as well as information characterizing thestimulator 20, may be entered and stored in the system 10 using thekeyboard 14, or other suitable data-entry input/output (I/O) device.Alternatively, the electrode array and electrode information may bepreprogrammed into the system 10. The electrode array position data maybe determined using any suitable procedure, such as X-ray, xerography,fluoroscopy, or other imaging techniques, which position data is thenentered into the programming system.

The programming screen shown in FIG. 4 includes an “Implant Selection”button 38. By clicking on the Implant Selection button 38 (or pressingon the button when a touch-sensitive screen is employed) displayed onthe display screen 16, a drop-down list appears containing data thatcharacterizes the available stimulators 20 and electrode array designs.Using the joystick 12 or keyboard 14 or other I/O device, theinformation for the implanted unit may be chosen from the list and inputinto the system. If the information for a particular unit is not on thelist, the information can be entered. Pressing the “Advanced” button 40provides access, through an appropriate menu selection, to advancedprogramming features such as manual electrode selection, burstprogramming, stimulation ramping, and other features commonly used inthe art. The information is provided to the programmable memory 67 (FIG.2) of the stimulator 20 in order to control the delivery of electricalpulses to the desired electrodes 24.

Once information characterizing the electrodes 24 and stimulator 20 areinput into the system, a simulated display appears on one portion (e.g.,the right portion as shown in FIG. 4) of the programming display screen16 that illustrates the placement and relative position of each of theelectrodes 24 included within the array 23 of electrodes relative to thepatient's spinal column 26. A simulated display 32 of the electrodearray pattern 23 thus appears on the display screen 16 just as thoughthe programmer could view inside the patient to see the electrodeplacement on or near the spinal column. For the representative electrodearray 23 shown in FIG. 4, two columns of electrodes 24 are used, eachhaving six electrodes. Thus, the particular electrode array 23 shown inFIG. 4 has a total of twelve (12) electrodes. Each electrode in eachcolumn is spaced apart from adjacent electrodes along the same column.It is to be emphasized that the type of array shown in FIG. 4 isexemplary of only one type of many different types of arrays that may beused. Often, two or more leads are implanted, each having its own array.In such instance, the information (two or more leads with respectivearrays) is entered into the system and accounted for in the programmingand visual displays. What is relevant to the programmer is which lead(s)is (are) being used (to determine the electrode array layout, how thelead(s) is (are) oriented with respect to one another and the spinalcord, and which pulse generator within the implant is driving thestimulation electrode contacts.

The basic functions addressed by directional programming in accordancewith the present invention include moving, concentrating, and focusingthe stimulation field. While these functions could be separatelycontrolled by several input devices, a preferred embodiment of thepresent invention advantageously minimizes hardware and software buttonsby combining all these functions into one device, e.g., a singlejoystick device 12, thereby providing simplification in both design anduse. The manner in which the preferred joystick device addresses each ofthese functions is depicted in FIG. 5A.

Any number of electrodes 24, out of the total available, may be formedinto an electrode group 45 which can be displayed as a stimulation field36. Through use of an additional data input device, e.g., selectorbutton 42, the number of electrodes within the electrode group 45 can beincreased or decreased. Such action (increasing or decreasing the numberof electrodes in the group) redistributes, or concentrates, thestimulation current over a greater of smaller area.

The selector 42, for the embodiment shown in FIG. 3, comprises a pair ofarrow buttons (up/down) that are located on top of the joystick 12. Ofcourse, such selector 42 could also be separate, i.e., accessed fromkeyboard buttons. In a preferred implementation, the number ofelectrodes in a stimulation group 45, from 2 to n, where n is an integergreater than or equal to three, is initially determined byincrease/decrease input from the selector, rather than by manuallyselecting electrodes.

Once the starting number of electrodes (concentration of stimulation) isdetermined, it is then focused and/or moved by the directional input ofjoystick 12. Selection software algorithms, stored in memory 54, work inconjunction with the position defined by the joystick 12, and/or otherdirectional instructional means, to configure and combine the electrodes24 into the electrode group creating the stimulation field 36. As thephysician or patient maneuvers the joystick 12, the resultingstimulation field 36 and/or the selected electrodes can be visualized ondisplay 32 (e.g., by a different color, by shading, by a dashed lineencircling the selected electrodes, or the like.) The preferred mannerin which the current stimuli is applied through the electrodes in thestimulation group 45, and more particularly the manner in which thecurrent stimuli increases or decreases as the stimulation field isincreased or decreased, is described more fully below.

In FIG. 5B, for example, an illustration is given of two columns of fiveelectrodes 24. The selected group 45 of electrodes comprises twoelectrodes in the left column (second and third from the bottom), whichare set to a “+” polarity, and one electrode in the right column (secondfrom the bottom) which is set to a “−” polarity. This polarity andgrouping creates an electric field which will cause electrical currentto flow from both of the “+” electrodes to the single “−” electrode,which in turn defines a stimulation area 36 that is nearer to the rightcolumn than the left column, and that tends to be more concentratednearer the “−” electrode.

Next, as illustrated in FIG. 5A, it is seen that the joystick 12 (orother directional programming device) can move a group selection ofelectrodes up and down within the array, which thus moves the field 36up or down the spinal cord respectively. As the joystick 12, or otherdirectional input device, is maneuvered forward, for example, thecurrent field is steered up the spinal cord. This occurs, in oneembodiment, by moving the selected group of electrodes up one levelalong the array. Because stimulation is generally associated with thecathode, or negative polarity electrodes, the stimulation can also bedistributed among a group of electrodes by changing positive polaritiesto negative, and negative to positive, in the path of the directionprogramming within the group.

For even finer control of current steering, the amplitude of a group 45of electrodes which includes more than a single anode and cathode isassigned a “group amplitude”. The group amplitude is, in effect, acumulative amplitude and might be, e.g., 5 mA, which is the absolutevalue total for all of the cathodes (−electrodes) in a singlestimulating group. Thus, if a group of electrodes consists of fourelectrodes, including 2 anodes and 2 cathodes, the default value forsuch group might be −2.5 mA on each negative electrode, and +2.5 mA oneach positive electrode. As the joystick 12 moves the stimulation areain an upward direction, the amplitude distribution is graduated to thehigher anodes and cathodes until the lower anodes and cathodes areeventually turned off, after which the next higher electrodes startincreasing in amplitude as the joystick 12 is held in the forwardpotion. This process is explained more fully below.

By way of illustration, reference is made to FIG. 6A, which shows a fourelectrode group 45. Electrodes A and F each have −2.5 mA flowing to theelectrode, totaling −5 mA, and electrodes B and E each have +2.5 MAflowing from the electrode. Hence, each polarity totals an absolutevalue of 5 mA. As the joystick 12 is moved forward, causing theelectrodes C and G to be included in the group 45, and the electrodes Aand E to be excluded from the group 45, the current flowing throughelectrode B and F each increases toward an absolute value of 5 mA, whileelectrodes A and E decrease toward 0 mA. As soon as electrodes A and Ereach zero, electrodes C and G begins to increase toward an absolutevalue of 5 mA, while the electrodes B and F decrease toward zero. Inthis manner, the joystick 12 is able to steer the current up or down toa desired stimulation area 36. Note that current may also be steered inthis manner left or right, although this is only possible when there areat least two rows of electrodes. The objective of directionalprogramming is simply to steer current in the direction desired withinthe constraints of the electrode array(s) and pulse generator(s) byautomatically configuring electrodes by defining or controlling thestate (positive, negative, or off) of each electrode and by distributingcurrent, including amplitudes, among the ON electrodes.

Another function available with directional programming, which could belinked to a separate direction input mechanism, is illustrated in FIG. 5as field “spread” on the off-axis directions of a combined joystick 12.This directional input of the “spread” feature increases or decreasesthe current path, or the distance between selected electrodes. Thisaffects the stimulating field by having a broader expanded field or amore focused field. To spread the field in a particular direction, forexample, certain electrodes are locked in position, while others aremoved in the direction of the spread desired. Referring to the fourelectrode group identified in FIG. 6A, including electrodes A, B, F andE, the following process is used: to move the spread up, electrodes Aand E are held, while F and E are switched to C and G. In this manner,the positive to negative current path is lengthened, and the spread isincreased. It is to be understood that there are many ways to organizethe effect of directions to electrode configuration changes, all ofwhich are included within the spirit of the invention. It is the use ofa directional input device, or directional signals however generated, toautomatically reconfigure electrodes for directing or steering current,whether to move a field, spread/focus a field, or concentrate a fieldfor stimulation, that comprises the essence of the invention.

The constraints of the directional programming for the selection ofelectrodes depends on the lead style being used as well as the pulsegenerator. For example, a single in-line lead, such as is shown in FIG.6C, would not have any left-to-right steering mobility. On the otherhand, if two in-line leads are placed with electrodes in parallel, whichwould be input to the system, there would be left-to-right currentsteering possibilities. Likewise, use of existing pulse generators, suchas the Itrel II pulse generator manufactured by Medtronic, would not beable to include more than four electrodes in a group.

The electrical current information for the electrode group 45 istransmitted by the RF signals to a receiving coil inside the stimulator20 by a transmission coil 28 connected to the programmer 10 via a cable30 (as shown in FIG. 3). As has been indicated, the advantage of usingthe joystick 12 (or other directional programming device) is that theclinician never has to manually select each possible combination ofelectrodes 24, or manually select each possible combination ofelectrodes 24, or manually input the desired stimulation parametersassociated with each electrode selection. The initial parametersassociated with the stimulation can be set, and then, by using thejoystick 12, different electrode combinations can be selected while theclinician observes an immediate response from the patient, oralternatively the patient can directly operate the system. This allowsthe operator to move toward or away from certain joystick 12 maneuvers,with the electrical current for each of the electrodes 24 beingreconfigured automatically with the joystick (directional programming)software.

In one embodiment, the operator adjusts the pulse amplitude (inmilliamps, “mA”), the pulse width (in microseconds, “μS”), or pulserepetition rate (in pulses per second, “pps”) of the pulses that aredelivered to the group of electrodes selected by the joystick 12 usingthe simulated “slide switches” 35, 37 and 39 displayed on the screen 16.The amplitude is set for a “stimulation” channel, a single but alterablestimulation field. The channel amplitude is distributed among electrodes(+/−) as they are added or subtracted into the channel's electrode groupwith respective polarities. In this manner, the operator may simplymaneuver the selected group 45 of electrodes to a desired area using thejoystick (or other directional device), and make adjustments in thepulse width, pulse amplitude, and pulse repetition rate, and observewhether favorable or unfavorable results are achieved.

For some embodiments, the configuration software automatically makesconfiguration adjustments as a function of the stimulation parametersselected. For example, if the amplitude of the current stimulationpulses is set to a high value, then the size of the group 45 ofelectrodes included within the selected group may swell or increase,e.g., to four or five or more electrodes (from a nominal group size of,e.g., three electrodes); whereas if the amplitude of the currentstimulation pulses is set to a low value, the size of the group 45 ofelectrodes included within the selected group may decrease, e.g., to oneor two electrodes.

In one embodiment, the configuration software selects the size of thegroup 45 of electrodes in the manner illustrated in FIG. 5A. As seen inFIG. 5A, the electrodes are configured to move the stimulation field upby moving the joystick arm up, to move it down by moving the joystickarm down, to move it right by moving the joystick arm right, and to moveit left by moving the joystick arm left. The relative size (number ofelectrodes within the group) of the group of electrodes is set bydepressing one of two selector buttons 42 (increasing or decreasing) ontop of the joystick arm (or otherwise positioned near thedirectional-programming device). The selected size may then be spread upand left by moving the joystick arm up and to the left; may be spreaddown and left by moving the joystick arm down and left; may be spreaddown and right by moving the joystick arm down and right; or may bespread up and right by moving the joystick arm up and right.

FIG. 6B illustrates an alternative embodiment of one type of electrodearray 23′ that may be used with the invention. In FIG. 6B, theindividual electrodes A, B, C and D included in the left column ofelectrodes are offset from the individual electrodes E, F, G and Hincluded in the right column of electrodes.

FIG. 6C depicts yet another embodiment of an electrode array 23″ thatmay be used with the invention. In FIG. 6C, electrodes E1, E2, E3, E4,E5, E6, E7, and E8 are arranged in a single column to form an in-lineelectrode array. The in-line array shown in FIG. 6C is electricallyconnected with a pulse generator 20′. The case of the pulse generator20′, or at least a portion of the case at the pulse generator 20′, maybe electrically connected as a reference electrode, Eg (see FIG. 2). Byway of example, a group 45′ of electrodes may include electrodes E4, E5and E6, with electrodes E4 and E6 being positive electrodes, andelectrode E5 being a negative electrode. The group 45′ could “swell” toa larger group by including electrodes E3 and E7 in the group.Alternatively, the electrode group 45′ could decrease to a smaller groupby removing electrode E3 or electrode E7 from the group. The electrodegroup 45′ could move up the electrode array by gradually deletingelectrode E6 from the group while at the same time gradually includingelectrode E3 in the group, until such time as the group includeselectrodes E3, E4 and E5. Continued movement of the electrode group upthe array could continue by gradually deleting electrode E5 from thegroup while at the same time gradually including electrode E2 in thegroup. The inclusion and deletion of electrodes within the group ispreferably accomplished in small steps, while maintaining currentbalance and perceived stimulation levels, as explained more fully below.

The present invention is preferably practiced using a stimulatingsystem, e.g., an SCS system, that includes individually programmableelectrodes. That is, it is preferred to have a current generator whereinindividual current-regulated amplitudes from independent current sourcesfor each electrode may be selectively generated. Although this system isoptimal to take advantage of the invention, other stimulators that maybe used with the invention include stimulators having voltage regulatedoutputs. While individually programmable electrode amplitudes areoptimal to achieve fine control, a single output source switched acrosselectrodes may also be used, although with less fine control inprogramming. Mixed current and voltage regulated devices may also beused with the invention. With a single output source, the finestshifting of amplitude between electrodes is a total shift of the fieldfrom one or more selected electrodes to the next configuration. With twooutput sources, finer control can be achieved by gradually reducingoutput on one or more electrodes to be deleted from the group, andproportionately increasing the outputs on the electrodes to be includedwithin the group. When as many output sources as electrodes areavailable, even finer shifting (smaller steps) may be achieved on eachof the electrodes included in the shifting process.

In accordance with one aspect of the invention, a method of programmingis provided wherein current (via current or voltage regulation) isshifted between two or more electrodes. The method begins with settingan amplitude level, in addition to other parameters such as pulse widthand rate, as is currently done in practice. Advantageously, theamplitude level may be set in one of two ways: (1) using a fixed outputvalue (standard method), or (2) using normalized output values (a newmethod).

As indicated, the amplitude level may be set using a fixed output value,such as 3 mA, or 3 Volts. Although it is possible to use a fixedamplitude value with the programming method described herein, there aredisadvantages that will be apparent as the programming method is furtherdescribed.

The amplitude level is preferably set using normalized output values, asdescribed, e.g., in the '167 provisional application, previouslyreferenced. This approach provides a normalized amplitude acrosselectrodes with respect to patient thresholds. To better understand thenormalized amplitude approach, it will be helpful to review howprogramming is currently performed. Currently, a patient or clinicianadjusts the actual amplitude value, e.g. in voltage units within therange of the system capability. For example, the output on electrode E1may be set to 3 volts, the output on electrode E2 may be set to 4 volts,and the like. However, an electrode array with n electrodes in a row(E1-En) on the spinal cord will likely have a variety of perceptionthresholds and maximum comfortable thresholds for each possibleelectrode at a given location in each possible combination. In a systemthat has an output range of 1-10 mA, for example, a patient might firstperceive stimulation at 1 mA on E1 and might begin to feel uncomfortablestimulation at 5 mA. Likewise, electrode En might have a perceptionthreshold (PT) of 2 mA and a maximum threshold (MT) of 4 mA. Thus, thefirst perception level of stimulation, or the lowest perceptiblestimulation, may be different for electrode E1 than it is for electrodeEn; and the highest comfortable level of stimulation may also bedifferent for electrode E1 than it is for electrode En. If a fixed valuewere to be set, e.g., 3 mA, and switched between electrodes, not onlywould the location of sensation change, but so would the intensity ofthe perceived stimulation.

The present invention, through use of normalized output levels,advantageously normalizes stimulation levels to perception. That is, aprogrammable amplitude range is utilized having an arbitrary scale,e.g., 0-10 (or min-max), with n steps. This arbitrary scale is thencorrelated to an actual current or voltage value. A zero level is equalto zero mA; a level one (or minimum level) is set to be equal to theperception level; a level 10 (or maximum level) is set to be equal to amaximum threshold level (i.e., the threshold level at which the patientbegins to experience discomfort or pain). Thus, for example, setting theoutput of a given electrode to level 5 would place the output currentstimulus (or voltage) so as to proportionately fall in the middle of thecomfort zone for each electrode. Thus, using normalized intensity levelsbased on thresholds to control stimulation output comprises an importantpart of the present invention. In order to use normalized intensitylevels based on threshold, a brief recording of the thresholds to beused in the programming equipment must initially be made.

In addition, electrode thresholds vary with the anodic and cathodiccombinations. Typical electrode configurations are monopolar (oneelectrode paired with the implantable pulse generator, IPG, caseground), bipolar (a relatively close +− pair of electrodes), andmultipolar (e.g. +−+). It is generally impractical to collect and recordeach threshold of each electrode in every possible combination to use inthe programming of a stimulator. However, it has been found in thespinal cord that the bipolar thresholds, monopolar thresholds, andtripolar thresholds follow a similar trend. Thus, it is possible torecord a minimal subset of thresholds, and then interpolate or estimatethe remaining thresholds for each possible combination.

Normalizing amplitude for programming a stimulation system, such as anSCS system, is thus an additional feature of the present invention,although it is not required to practice the invention. Normalizedamplitude programming offers an advantage because in order to recombineelectrodes without manually resetting the amplitude to ensure acomfortable stimulation level, the normalized amplitude will aid inautomatically calculating actual current or voltage amplitudes forrecombined electrodes. Stimulation perception is also a product of pulsewidth, however, and pulse width should also be included in any thresholdestimations or adjustments. Also, it should be noted that the samenormalizing method may be used for motor thresholds instead ofperception thresholds in applications where motor function is beingachieved (FES).

Thus, it is seen that the present invention includes, inter alia, thesetting of amplitudes and/or pulse widths during programming on selectedelectrodes based on programming normalization to perception values, withthe ability to discriminate between various configuration types toadjust the threshold ranges. That is, the invention includes a means toincrease the amplitude and/or pulse width, a means to record thethresholds for selected electrodes, and a means to estimate and/orinterpolate thresholds for unrecorded electrodes in any givencombination.

A preferred means to accomplish the above functions includes a softwareprogram that steps the patient or clinician through a process thatrecords a minimum set of threshold values required to estimate theremaining thresholds to be used in the programming of the stimulator(i.e. a software wizard or a threshold user interface screen). Anothermeans comprises use of a hardware device that has a location to identifythe minimum and maximum thresholds for a given set of electrodes.

Currently, to Applicants' knowledge, threshold data is not recorded norused to drive the programming of multiple electrode combinations.Instead, an electrode combination is selected, the amplitude is turnedup from zero to a comfortable level, the patient responds to where thestimulation is felt, and the process is repeated for as manycombinations as can or would be tried. This is true for manual selectionor computer generated electrode selections.

An example of an equation that may be programmed into a processor andused by the invention to normalize amplitude levels is as follows:

X=Amplitude Level (0-10), 0 level=0 mA

I_(i)=Current Amplitude, mA for electrode i of n

P_(i)=Perception Threshold, mA for electrode i of n

M_(i)=Maximum Threshold, mA for electrode i of n

F_(i)=Fractional stimulation (±100%), % on electrode i of n

For all cathodes (i.e. F_(i)<0):I _(i) =F _(i) ×P _(i) ×X for 0≦X≦1andI _(i) =F _(i)×[{(M _(i) −P _(i))/9}×(X−1)+P _(i)] for X>1.

Note that:If X=0, I_(i)=0If X=1, I _(i) =P _(i) ×F _(i)If X=10, I _(i) =M _(i) ×F _(i)

The total current for all cathodes is then:$I_{cathode} = {\sum\limits_{{i = 1},{F_{i} < 0}}^{n}\quad I_{i}}$

The current for anodes (i.e. F_(i)>0) is:I _(i) =−F _(i) ×I _(cathode)

An example of output currents for different values of X using simplemonopolar stimulation is as illustrated below in Table 1:

TABLE 1 Electrode E1 E2 E3 E4 E5 E6 E7 E8 CASE P_(i) (mA) 2 3 3.3 2 2.22 3 4 NA M_(i) (mA) 10 12 12.7 11 10 9 11 12.7 NA F_(i) (%) −100% 100%I_(i) (mA) X = 0 0.00 0.00 X = 0.5 −1.50 1.50 X = 1 −3.00 3.00 X = 5−7.00 7.00 X = 10 −12.00 12.00

An example of output currents for multi-cathode stimulation is asdepicted in Table 2, presented below:

TABLE 2 Electrode E1 E2 E3 E4 E5 E6 E7 E8 CASE P_(i) (mA) 2 3 3.3 2 2.22 3 4 NA M_(i) (mA) 10 12 12.7 11 10 9 11 12.7 NA F_(i) (%) −90% −10%100% I_(i) (mA) X = 0 0.00 0.00 0.00 X = 0.5 −1.35 −0.17 1.52 X = 1−2.70 −0.33 3.03 X = 5 −6.30 −0.75 7.05 X = 10 −10.80 −1.27 12.07

A more complex example, involving multipolar stimulation, is shown inTable 3:

TABLE 3 Electrode E1 E2 E3 E4 E5 E6 E7 E8 CASE P_(i) (mA) 2 3 3.3 2 2.22 3 4 NA M_(i) (mA) 10 12 12.7 11 10 9 11 12.7 NA F_(i) (%) 10% −90%−10% 90% I_(i) (mA) X = 0 0.00 0.00 0.00 0.00 X = 0.5 0.10 −0.90 −0.110.91 X = 1 0.20 −1.80 −0.22 1.82 X = 5 0.60 −5.40 −0.57 5.37 X = 10 1.09−9.90 −1.00 9.81

Another example of this implementation is:

-   E1: P=1 mA, M=4 mA-   E2: P=2 mA, M=4 mA-   If X=5, then:-   E1=2.5 mA or E2=3 mA-   If X=5 then:    If stimulation is 100% on E1, then E1=2.5. mA    If stimulation is 90% on E1 and 10% on E2, then E1=90%*2.5 mA and    E2=10%*3 mA.    Thus, if the level is set to X=5, and a shifting process moves the    current field from E1 at 100% stimulation to 90% E1 and 10% E2 then    the normalized values are proportionately shifted. The maximum shift    would be from 100% *E1 to 100% *E2.

If normalized values are not used and X is set to 3 mA

Then:E 1*100%=3 mAOr,E 1 (90%) and E 2 (10%): E 1=2.7 mA and E 2=0.3 mA.

A key part of the invention includes using a programming scheme toautomatically switch electrode combinations, current distributions, etc.A suitable input mechanism, such as a joystick, or other input device,such as voice or sensor activation, may be used as the control input.Automatic preset shifting may also be used. In accordance with theinvention, a suitable control mechanism (driven in software, hardware,and/or mechanical) is used to direct or steer stimulation (a currentfield) by combining anodic and cathodic electrodes in whole or in partof a given output. This requires independently programmable electrodeoutputs for at least two electrodes, and optimally n outputs for nelectrodes. To illustrate, assume electrode E1 is selected as a cathodeand electrode E3 is selected as an anode, either by default or manualselection. After the amplitude level is set (normalized or constant),current can be steered by automatically combining electrodes withvarious current distributions (depending on the stimulators capability).In a single row electrode, such as is illustrated in FIG. 6C, steeringcan only occur in the same axis. In a dual row (or more) electrodearray, such as is shown in FIGS. 6A and 6B, an x-y axis can be steered.Additionally, a z axis can be included (depth of penetration bymodulating intensity).

To shift current, the amplitude on a particular electrode is reducedproportionately to another electrode's increase. If, for example, acathode electrode E1 has an amplitude of 3 mA (or 3V), the output can bereduced to 90%, 80%, etc., down to zero while another electrode E3 isincreased to 3 mA starting from zero and increasing to 100%. The currentsummation in this case is always 3 mA.

The same shifting of current may also be accomplished with a normalizedamplitude distribution among electrodes. Instead of applying aproportional increase or decrease on electrodes based on a constanttotal amplitude, however, the increase is proportional to the normalizedlevel. This enables the shifting of current to stay at a relativelyconsistent perceptual intensity as the current field is directed to newlocations. If, for example, a normalized “Level 5” (out of 10) is set,as cathodic current flow, and is shifted from the location of electrodeE1 to the location of electrode E2, the intensity applied to electrodeE1 beginning at 100% would have a value in the middle of the comfortablerange (e.g., half way between the perception threshold and the maximumthreshold). Should the threshold range for electrode E1 be 1 mA to 3 mA,then level 5 for electrode E1 would be 2 mA. Likewise, if the thresholdrange for electrode E2 is 3 mA to 5 mA, then level 5 for electrode E2would be 4 mA. Thus, as current is shifted from electrode E1 toelectrode E2 in a gradual manner, electrode E1 would be reduced bypercentages of 2 mA (at level 5) as E2 is proportionately increased toits level 5, or 4 mA. Such can result in differing current summations asthe current field is shifted, but there should be little or noperceptual change in intensity felt or sensed by the patient. If aconstant current value of 4 mA were to be used instead of a normalizedvalue, then as the current is shifted back from E2 to E1, the maximumthreshold for the patient would be exceeded and could prove veryuncomfortable for the patient. Thus, it is seen that by using a singlecurrent value, the current shifting could result in fluctuationintensity perceptions that can drop below the perception threshold orexceed the maximum tolerable threshold. To avoid this undesirableresult, frequent adjustments in amplitude would have to be made duringthe shifting process. That is why use of the normalized value ispreferred for the present invention: total amplitude adjustments may beautomated while maintaining a comfortable stimulation perception.

It is noted that non proportional shifts could also be made, but suchwould be less optimal and would defeat the purpose or ease ofcalculation. However, if the shifting differences are minimal, suchdifferences would not likely be perceived. An example of a nonproportional shift is as follows: reducing E1 by 10% while increasing E2by 20%, then reducing E1 by 20% while increasing E2 by 10%. Each shiftis not proportional, but the shift ultimately results in a shift fromelectrode E1 to electrode E2, as is the case with proportional shifts.

Furthermore, it is noted that stimulation is typically driven bycathodic current. However, the positive and negative settings must equalzero. Any shifting of anodic electrode values must total the current onall of the cathodic electrodes, not perception thresholds. When shiftingcurrent fields using normalized levels, the combined current willfluctuate. Thus, proportional shifting of anodic values would not bebased on the perception level, but on the total cathodic current. Ifdriven by anodic current, then the opposite is true.

To move current from one location to another without having to set upeach combination in a discretely tested process comprises a key elementof the invention. Such is accomplished through use of a continuouscurrent shifting process where stimulation is not interrupted. Severalimplementations of the continuous shifting process may be used. Forexample, the shifting process may include an algorithm that responds toan input signal indicating a directional move to calculate the nextconfiguration to move current. The steering input device is used toindicate the next location of data to be used to calculate the electrodeconfiguration. The data may be extracted from a “solve for” formula, orby locations on one or more tables advanced by the input device, or acombination of formulas and tables. In any case, the next configurationis predicated on, or calculated from, the previous configuration. Eachinput move configures the electrodes and distributes the current.

An example of a current shifting table-based algorithm used to shiftcurrent horizontally across an electrode array is illustrated in FIG. 7.In FIG. 7, as well as in FIGS. 8 and 8A-8Q (which show a table-basedalgorithm used to shift current vertically), explained below, the grayor shaded portion of the table represents that portion of cathodicamplitude value that is based on the normalized constant value set,whereas the white (non-shaded) portion of the table represents thatportion of anodic current that is based on the sum of all the cathodiccurrents. The sequence of numbers arranged in a column along the leftside of the table represent the discrete steps that are utilized in theshifting process, which steps are controlled by the user through anappropriate input mechanism, e.g., a joystick or equivalent device.Thus, in FIG. 7, at step number 1, the stimulus current (normalized to“1.0” in the table) flows from the anode (+) to the cathode (−) on theleft side of the array. At step number 2, the anodic current (+) on theleft is decreased 10%, the anodic current (+) on the right side of thearray is increased the same amount, while the cathodic current (−)remains the same. Following this pattern, the anodic current (+) isgradually shifted from the left side to the right side while thecathodic current (−) is held at a constant value. Thus, at step number11, all of the anodic current (+) has shifted to the right, while all ofthe cathodic current (−) remains on the left. Then, beginning at step12, the cathodic current begins to shift in discrete steps of 10% fromthe left side to the right side, while the anodic current shifts insimilar amounts from the right side back to the left side. Thiscontinues until at step 21 all of the cathodic current (−) has beenshifted to the right side and all of the anodic current (+) is back tothe left side. Then, while holding the cathodic current (−) constant onthe right side, the anodic current (+) is shifted back to the right sidein discrete steps of 10%, until at step 31 all of the anodic current (+)has been shifted back to the right side, resulting in a complete shiftof the stimulus current from the left side of the array to the rightside.

It should be noted that in the shifting algorithm shown in FIG. 7, aswell as that shown in FIGS. 8 and 8A-8Q, that the illustrated discretestep size of 10% is only exemplary. In practice, the step size could besmaller or larger than this amount, as desired.

In a similar manner, FIGS. 8 and 8A-8Q illustrate an exemplarytable-based algorithm that may be used to shift current verticallywithin an electrode array, e.g., up or down an in-line array of the typeshown in FIG. 6C. For purposes of the example shown in FIGS. 8 and8A-8Q, it is assumed that monopolar stimulation is present at electrodeE1 (paired with the case electrode), and that it is desired to shift thestimulation vertically so that eventually monopolar stimulation isachieved at electrode E8 (paired with the case electrode). Starting atstep number 1 in FIG. 8A, all of the anodic current (+) flows from thecase electrode, and all of the cathodic current (−) flows to electrodeE1. The anodic current (+) flowing from the case electrode is graduallydecreased in small discrete steps of, e.g., 10%, while the anodiccurrent (+) flowing from electrode E3 gradually increases in the samestep sizes, until at step 11, all of the anodic current (+) has beenshifted to electrode E3. Then, beginning at step 12, the anodic current(+) flowing from electrode E3 is gradually decreased in discrete stepsof 10%, while the anodic current (+) flowing from electrode E4 graduallyincreases in the same step sizes, until at step 21 (FIG. 8B), all of theanodic current (+) has been shifted to electrode E4. Beginning at step22 the cathodic current (−) flowing to electrode E1 is graduallydecreased in discrete steps of 10%, while the cathodic current (−)flowing to electrode E2 is gradually increased in discrete steps of thesame value, while at the same time the anodic current (+) flowing fromelectrode E4 is gradually decreased in discrete steps of 10%, while theanodic current (+) flowing from the case electrode increased in discretesteps of the same value. Following this process, at step number 31, allof the cathodic current (−) has been shifted to electrode E2, while allof the anodic current (+) has been shifted back to the case electrode.Then, beginning at step 32, the anodic current (+) is gradually shiftedto a second case electrode, until at step 41 all of the anodic current(+) has been shifted to the second case electrode.

Following a process similar to that described above, the cathodiccurrent (−), which is generally considered as the current responsiblefor achieving a desired stimulation, is gradually shifted in smalldiscrete step sizes, as shown in the balance of FIG. 8B, and continuingthrough FIGS. 8C-8Q, at step number 291 of FIG. 8Q, the cathodic current(−) has been shifted vertically all the way to electrode E8 and theanodic current (+) is all flowing from the case electrode (monopolarsimulation).

It is to be emphasized that the equivalent of using formulas and/ortables to configure electrodes and distribute current may be achievedthrough other means, such as the use of a mechanical switching matrixmechanically controlled by an input steering device, such as a joystick.It is submitted that those of skill in the art could readily fashionsuch a switching matrix, given the teachings provided herein.

Turning next to FIG. 9, there is shown a block diagram of the softwarearchitecture used in a preferred embodiment of the present invention. Asseen in FIG. 9, a core program 100 invokes other programs, e.g.,subroutines and/or databases, as required to assist it as thestimulation system carries out its intended function. The core program100 includes two sections: a main section 102′ that invokes a mainprogram 102 where the underlying programs that control the operation ofthe SCS system reside, and a navigator section 104′ that invokes aNavigator Wizard program 104 where set up programs reside that aid theuser as he or she initially sets up, i.e, programs, the system. That is,the Navigator Wizard program 104 facilitates programming the mainprogram 102 so that the main program 102 has all the data and parametersettings it needs to carry out its intended function.

When invoked, the main program 102 provides stimulation pulses to thepatient at selected electrode locations with stimulation pulses having aselected amplitude, pulse width, pulse repetition rate, and othercontrol parameters. Being able to readily determine the optimum locationwhere the stimulation pulses should be applied, and the parametersassociated with the applied stimulation pulses (amplitude, width, rate)is the primary focus of the present invention.

Data files 106 and 108 track the patient's history, and patient file 110provides patient data information. The information contained in patientfile 110, e.g., patient name, address, type of stimulator, serial numberof stimulator, etc., is generally entered by the physician or othermedical personnel at the time the patient is first fitted with the SCSsystem. The data in the history file 108 keeps a chronology of when thepatient visited the SCS physician and for what purpose, while the datain the selected visit file 106 provides detail data regarding whatoccurred during a given visit.

An exemplary patient information screen display that is generated on thedisplay screen 16 of a suitable programming device 10 (FIGS. 1A, 2 and3) when patient information is entered or reviewed is shown in FIG. 10.Such patient information display allows information such as the patientname, birthday, purpose of visit, diagnosis resulting from the visit,lead (electrode) type, area of pain, and the like, to be displayedand/or entered into the system. Included on the particular screen shownin FIG. 10 is a drop down menu 126 that allows the user to specify thetype of electrode array that the patient has, e.g., a single in-linelead, two in-line leads positioned end to end, two in-line leadspositioned side by side, and the like.

Referring back to FIG. 9, a pain map file 112 contains the needed datafor allowing the main programs 100, 102 to display a map of thepatient's body. Using this map, the patient, or other programmingpersonnel, may select those areas of the body where pain and/orparesthesia is felt.

An electrode file 114 stores data that defines the types of electrodesand electrode arrays that may be used with the SCS. Using the data inthe electrode file 114, the physician or other programming personnel,can define the electrodes available through which stimulation pulses maybe applied to the patient. Further, diagnostic testing of the availableelectrodes may be performed to verify that an electrode which should beavailable for use is in fact available for use.

A measurement file 116 stores and tracks the perception threshold andmaximum comfort threshold that are either measured using the navigatorwizard program 104, or calculated based on an interpolation of measureddata by the main program 100.

An advanced program file 118 provides various programs and data neededto perform advanced functions associated with operation of the SCSsystem. In general such advanced functions are not that relevant to thepresent invention, and are thus not described in detail. The advancedprogram file 118 further provides a location where future enhancementsfor the SCS system operation may be stored and updated. For example,should an improved interpolation technique be devised to calculatethreshold data stored in the measurement file 116, then such improvedinterpolation technique could be stored in the advanced program file118.

A key feature of the present invention is the use of a navigator wizardprogram 104. The wizard program(s) 104 provides a software interfacethat advantageously walks the user step by step through the measurementand programming process. Additionally, to make the process even easier,and enjoyable, the wizard may use a map, akin to a treasure map, whichis animated (akin to a video game) and incorporated into the fittingsoftware. Alternatively, the treasure map, or other type of map, may bepublished as a printed document. The purpose of the animated treasuremap, or printed document, or other software interface, as the case maybe, is to detail the fitting procedure, and more particularly tographically assist the clinician and patient as they search for theoptimum program settings that can be used by the system to best treatthe pain (or other neural condition) felt or experienced by the patient.

By way of illustration, the main steps carried out by a preferredmeasurement/programming wizard are illustrated in the flow diagram ofFIG. 11. In a first step (block 130), the user is directed to select astimulation channel. In some instances, there may be only onestimulation channel that is being used. In other instances, more thanone stimulation channel may be used. Once the channel has been selected,the user is prompted to click on the areas where pain is felt (block132). In one embodiment, this prompt is accomplished by displaying ascreen similar to that shown in FIG. 12A. As seen in FIG. 12A, a patientbody 158 is displayed having various stimulation areas 160 depicted. Byclicking on one of the areas 160, it is shaded, or colored, in anappropriate manner to indicate that it has been selected. This selectionactivates electrodes which are, as a first try, believed to be theelectrode(s) which can treat the pain area selected.

Referring back to FIG. 11, after the user has selected the areas wherepain is felt, the user is prompted to increase the stimulation leveluntil it is first felt (block 134). This step, in effect, measures thestimulation perception threshold. The user is prompted to measure thisthreshold, in one embodiment, by displaying a screen as shown in FIG.12B. Such threshold measurement screen provides instructions to the userin the upper left hand corner. It also displays three buttons, an OFFbutton 162, a decrease button 163, and an increase button 164. Bypressing (i.e., clicking) the OFF button 162, the user is able toselectively turn the stimulus current On of Off. Once on, the user canincrease or decrease the amplitude of the stimulation current using thebuttons 163 and 164. As he or she does so, a vertical bar graph 166,within a vertical window 165, increases or decreases in height, therebyproviding a visual indication of the relative level of the stimuluscurrent. Once the user has determined the level at which stimulation isfirst felt, the NEXT button 167 is pressed in order to advance to thenext step in the process.

Returning again to FIG. 11, the user next increases the stimulationlevel until the maximum comfortable level is determined (block 136).This step thus measures the maximum comfortable stimulation thresholdfor the patient on the selected channel. To aid in this process, in oneembodiment of the invention, a prompt screen as shown in FIG. 12C isdisplayed. The screen shown in FIG. 12C is essentially the same as theone shown in FIG. 12B except that different instructions are provided inthe upper left hand corner. As the user increases the stimulation levelto the maximum comfortable level, the bar graph 166 increases in height.Once the user has determined the maximum comfortable stimulation level,the NEXT button 167 is pressed in order to advance to the next step ofthe fitting process.

As seen in FIG. 11, the next step in the fitting process is to determineif more threshold measurements need to be taken (block 138). Typically,more than one electrode, or more than one grouping of electrodes, willbe associated with the selected pain site. Hence, the first thresholdmeasurements are taken for a first group of electrodes associated withthe site, and second threshold measurements are taken for a second groupof electrodes, and perhaps third threshold measurements are taken for athird group of electrodes. Typically, no more than about two or threegroups of electrodes are used to determine thresholds, although morecombinations than three could be measured for thresholds if desired. Ifevery possible electrode combination were measured, the fitting processwould take too long. Hence, in accordance with the teachings of thepresent invention, after two or three threshold measurements have beenmade, the threshold values for other possible electrode combinationsassociated with the selected pain site are calculated usinginterpolation or other suitable estimation techniques.

Once an adequate number of threshold measurements have been made (FIG.11, blocks 134, 136, 138), the user is instructed to manipulate thelocation arrow buttons to determine an optimal pain coverage. This stepis done, in one embodiment, by displaying a locator screen as shown inFIG. 12D. The locator screen includes, on its right side, controls forthe stimulation level, including an ON/OFF button 162, increase button164, decrease button 163, and stimulation level bar graph indicator 166,much the same as, or similar to, those shown in FIGS. 12B and 12C. Alsoincluded within the locator screen seen in FIG. 12D, in addition tospecific instructions in the upper left hand corner, is an up arrowbutton 169, a down arrow button 168, a left horizontal arrow button 171and a right horizontal button 171. The screen shown in FIG. 12D assumesthat only an in-line electrode is used, hence only the up button 169 andthe down button 168 are activated. (For electrode arrays that allowhorizontal movement, the right and left buttons 170 and 171 would alsobe activated.) As these locator buttons are pressed, the effectivestimulation site, schematically illustrated at area 172 in the center ofthe locator buttons, shifts up or down the electrode. Hence, through useof the locator buttons 168, 169, 170 and/or 171, the user is able tozero in on an optimal pain coverage location.

Once the user has located the optimal pain coverage location for theselected channel, the pulse duration is selected (FIG. 11, block 142).To assist the user in selecting the pulse duration, in one embodiment, apulse duration screen is displayed as shown in FIG. 12E. Such pulseduration screen includes instructions in the upper left hand corner ofthe screen, and stimulation level controls 162, 163, and 164 on theright side of the screen, similar to the previously-described wizardscreen of FIG. 12D. The pulse duration screen further includes arrowbuttons 173 and 174 which, when clicked, allow the user to decrease orincrease the stimulation pulse width. As adjustments to the stimulationpulse width are made, an analog knob 176, having a pointer 175, rotatesto the location indicative of the selected pulse width. For theselection shown in FIG. 12E, the pulse width is approximately 390microseconds. As an alternative to increasing and decreasing the pulsewidth using the arrow buttons 173 and 174, the user may also simplyclick and hold the mouse cursor on the knob 76, and then by moving thecursor, cause the knob to rotate to a desired pulse width selection.

Once the pulse duration, or pulse width, has been set, the next step isto select the pulse rate (FIG. 11, block 144). In one embodiment of theinvention, this step is prompted by displaying a rate screen as shown inFIG. 12F. Such pulse rate screen includes instructions in the upper lefthand corner of the screen, and stimulation level controls 162, 163, and164 on the right side of the screen, similar to the previously-describedwizard screens of FIGS. 12D and 12E. The pulse rate screen furtherincludes arrow buttons 177 and 178 which, when clicked, allow the userto decrease or increase the stimulation pulse rate. The rate selected isdisplayed as a number in the area 179. For the rate screen shown in FIG.12F, the rate has been set to 40 pulses per second (pps). Once the ratehas been set to a most comfortable level, the NEXT button 167 is clickedin order to advance to the next step of the fitting process.

The next step of the fitting process, as shown in the flow diagram ofFIG. 11, comprises defining where the stimulation is felt (block 146).This process is facilitated by displaying a patient FIG. 180 asillustrated in FIG. 12G. Once the FIG. 180 has been displayed, one area181 of the patient FIG. 180 is selected as the area where the patientfeels stimulation. While the area 181 is shown in FIG. 12G ascross-hatched, such is shown only for purposes of illustration in ablack and white drawing. Typically, the area 181 changes to a differentcolor, e.g., red, yellow, blue or green, when selected.

As part of step of selecting where stimulation is felt, some embodimentsof the invention further allow the user to select one of up to threedifferent stimulation settings as the best setting for that channel.Such selection is facilitated by displaying a navigation results screenas depicted in FIG. 12H. The navigation results screen shown in FIG. 12Hincludes instructions in the upper left hand corner of the screen, andstimulation level controls 162, 163, and 164 on the right side of thescreen, similar to the previously-described wizard screens of FIGS. 12D,12E and 12F. Also included are three selection buttons 182, 183 and 184,labeled “A”, “B” and “C” in FIG. 12H. Selection button “A” (button 182)selects a first set of stimulation parameters; selection button “B”(button 183) selects a second set of stimulation parameters; andselection button “C” (button 184) selects a third set of stimulationparameters. These different sets of stimulation parameters may bederived from the threshold measurements (FIG. 11, blocks 134, 136), thelocation manipulator adjustments (FIG. 11, block 140), and/or the pulseduration (FIG. 11, block 142) and pulse rate selections (FIG. 11, block144) previously made, or previously selected by the user. The ability toselect a “best” set of stimulation parameters in this manner offers theuser the chance to “feel” and “compare” stimulations based on differingsets of stimulation parameters in close proximity in time. In thisregard, the selection offered in the navigation results screen of FIG.12H is similar to the choice an optometrist or ophthalmologist offers apatient while testing vision when he/she asks the patient “which looksbetter, A, B or C?” as different lenses are switched in and out of theviewer through which the patient views an eye chart.

After the user has selected the “best” selection of stimulationparameters for the given channel (FIG. 11, block 148), he or she isoffered the choice to program additional channels (FIG. 11, block 150).In one embodiment, such choice is presented by way of a prompt screensuch as the screen depicted in FIG. 12J. Such prompt screen asks theuser whether he or she wants to program another channel, e.g., channel 2(see upper left hand corner), while presenting a display of thepatient's body 180′ wherein the other channel to be programmed isdefined. For the situation represented in FIG. 12J, channel 1 comprisesstimulation pulses applied to, or felt in, the right leg; while channel2 comprises stimulation pulses applied to, or felt in, the left leg. Ifthe user does want to program another channel, e.g., channel 2, then heor she clicks on a YES button 185. If the user does not want to programanother channel, then he or she clicks on the FINISH button 186.

Should the user indicate that he or she is finished, by clicking theFINISH button 186, then the user is provided the opportunity to reviewand/or verify the program settings that have been made (FIG. 11, block152). Such verification and review, in one embodiment, allows the userto select, inter alia, a chart, as shown in FIG. 13, that graphicallydisplays the normalized settings as a function of each electrodeposition. As seen in FIG. 13, for example, the minimum perceivedthreshold (level 1) is illustrated for all 8 electrodes. The minimumperceived threshold was measured only for electrodes E1, E4 and E8, andfrom these measurements the minimum perceived threshold was calculatedusing interpolation for the remaining electrodes E2, E3, E5, E6 and E7.Similarly, the maximum comfortable threshold was measured only forelectrodes E1, E4 and E8, and from these measurements the maximumcomfortable threshold was calculated using interpolation for theremaining electrodes E2, E3, E5, E6 and E7. The program settings screenshown in FIG. 13 further shows that electrode E2 is selected as thecathodic (−) electrode, with electrode E3 selected as the anodic (+)electrode, and with the stimulation current level being represented as avertical bar 166′. Such vertical bar 166′ shows that for the settingsrepresented in FIG. 13, the stimulation level on electrode E2 isapproximately half way (level 5 or 6) between the minimum (level 1) andmaximum (level 10) amplitude settings. The chart in FIG. 13 also showsthat a level 1 stimulation level on electrode E2 corresponds to astimulation current amplitude of about 5 ma, while a level 10stimulation level on electrode E2 corresponds to a stimulation currenthaving an amplitude of about 8.5 ma. Other buttons include in FIG. 13allow other settings to be verified, adjusted, or saved, in conventionalmanner.

Other of the data that may be reviewed and adjusted or modified, asdesired (FIG. 11, block 152), includes the parameter settings assummarized, e.g., on the screen shown in FIG. 14. Included in suchparameter setting display is a schematic representation 190 of thechannels on the left side of the screen. In the preferred embodiment, upto four independent channels may be provided by the SCS system. For thecondition represented by the parameter settings in FIG. 14, only onechannel is active (the one at the top of the channel windows, and it isprogrammed to provide a biphasic pulse). One of the channels is paused,and two of the channels have no electrodes selected, which means thesechannels are inoperable for this setting.

The parameter settings represented in FIG. 14 also include a schematicrepresentation of the electrode array. For the conditions represented byFIG. 14, two side-by-side in-line electrode arrays 191 and 192 are used,with staggered electrodes. The stimulation site selected is near thebottom of the arrays, as oriented in FIG. 14. The parameter settingsassociate with the active channel are also represented in FIG. 14, andmay readily be adjusted, if needed. As seen in FIG. 14, the stimulationlevel is set to “7”, the pulse width (or duration) is set to 350 μsec,and the stimulation rate is set to 50 pps. Any of these values may bereadily adjusted by simply clicking on to the respective slide bars 194,195 or 196 and moving the bar in one direction or the other. Before suchvalues can be adjusted, they must be unlocked, by clicking on therespective locked icon 197 at the bottom of the slide bar. Unlockingthese values for adjustment may, in some embodiments, require apassword.

FIG. 15 illustrates another type of screen that may be displayed as thechannel settings are reviewed and/or modified. For the most part, thescreen shown in FIG. 15 contains much of the same information as isincluded in FIG. 14. However, FIG. 15 further includes a patient display197 that allows selected areas on the patient, e.g., areas 198 and/or199, to be selected for receiving stimulus pulses.

Next, with respect to FIG. 16, a representation of a treasure map isdisplayed, which map may be used, in some embodiments of the invention,to aid the clinician and patient as the fitting process is carried out.The treasure map depicted in FIG. 16 highlights the path the patientmust follow to achieve a successful fitting of his or her SCS system,represented by a treasure chest, the ultimate goal of following the map.The treasure map shown in FIG. 16 may be displayed on the screen 16 ofthe programming device 10 (see FIG. 1A) and/or printed as a fold-outmap. Eye-catching illustrations may be positioned at various locationson the map, such as a sail boat carrying a trained, faithful andtalented crew of clinicians and other medical personnel to assure thatthe patient stays on course on route to the treasure. Other fun andinteresting information (not shown in FIG. 16) may also be included onthe map. When shown on a display screen, each of the main blocks, orsteps, included on the path to the treasure chest, may flash or belighted or change color as these steps are traversed by the patient.Sound bites may also be interspersed at key locations along the path tothe treasure to educate and entertain.

As is evident from FIG. 16, the fitting process involves much more thana single visit from the patient with the clinician. Rather, numeroussteps must be traversed, in a prescribed sequence, in order for thefitting to be successful. These steps are described more fully in thepreviously referenced '829 provisional patent application. As seen inFIG. 16, at least the following steps lie along the path to reach thetreasure—a successful fitting and a happy patient—: (1) a patientinterview office visit; (2) surgical planning; (3) percutaneouselectrode Implantation; (4) operating room (OR) fitting procedure; (5)First Post-surgical office visit; (6) trial stimulation parametersfitting; (7) trial stimulation period; (8) second post-surgical officevisit; (9) assessment of trial stimulation; (10) surgical planning; (11)IPG (implantable pulse generator) procedure; (12) FirstPost-IPG-Surgical Office Visit; and (13) final fitting.

As described above, it is thus seen that the present invention providesnumerous functions and meets various needs. These functions and needsinclude the following:

-   -   1. A programming system using an input device and control logic        (by software, hardware, or electrical design) to continuously        configure electrodes and current distributions in response to        the user controlled input device.    -   2. A method of stimulating where current shifting and electrode        configurations are determined in response to an input mechanism        controlled by the user, that interprets the shifting based on a        table, formula, or mathematical model.    -   3. A programming method where reconfiguring electrodes is        achieved without stopping stimulation to select the next        configuration to be tested.    -   4. A programming method where reconfiguring electrodes (or        current shifting) is achieved without stopping stimulation to        select the next configuration to be tested:        -   A. Using a table based approach (preset list of possible            sequences).        -   B. Using a “solve for” equation (or a mathematical model).    -   5. A neural stimulating system where electrodes can have current        split to unequal and independently determined levels on a single        channel.    -   6. A neural stimulating system wherein a threshold/maximal range        is used to normalize amplitude levels in a current summation        process to determine the amount of current that should be        applied on a given electrode in a group based on a given        “level”.    -   7. A method for changing electrode configurations and current        levels on selected electrodes of a neural stimulating system        while maintaining a relative intensity perception of the        stimulation.    -   8. A patient useable take-home programmer that interprets        normalized levels to proportionately increase or decrease        amplitude on the programmed group of electrodes, thereby        ensuring that the patient cannot exceed the maximum tolerable        level.    -   9. A method of programming where any change in distribution can        be implemented in the smallest obtainable change in stimulation        parameters on adjacent electrodes.    -   10. A method of programming where a transition from one        distribution of current or voltage amplitudes X={x₁, x₂, . . . ,        x_(n)} on n electrodes to a second distribution of current or        voltage amplitudes Y={y₁, y₂, . . . y_(n)} such that        ${\sum\limits_{i = 1}^{n}\quad( {x_{i} - y_{i}} )^{2}} < {{Maximum}\quad{{of}\quad\lbrack {\sum\limits_{i = 1}^{n}\quad( {x_{i} - y_{i}} )^{2}} \rbrack}}$    -   11. A system that must use the maximal resolution available to        the system at all points of its operation parameters, i.e. a 16        bit DAC system must use 16 bit resolution.    -   12. A user interface useable in a neural stimulation system that        visually represents the changing current field.    -   13. A user interface useable in a neural stimulation system that        uses consecutive windows in a “wizard” process to step the user        through each step in the fitting process.    -   14. A system that allows a clinician and the patient to quickly        determine the desired electrode stimulation pattern, including        which electrodes of a multiplicity of electrodes in an electrode        array should receive a stimulation current, including the        amplitude, width and pulse repetition rate of such current, so        that the tissue stimulator can be programmed with such        information.    -   15. An electrode selection/programming system that allows the        clinician to readily select and visualize a particular group of        electrodes of an electrode array for receipt of a stimulation        pulse current, and/or to allow different combinations of pulse        amplitude, pulse width, and pulse repetition rates to be applied        to the selected group.    -   16. A system that facilitates the programming of an implantable        tissue stimulator, having an array of stimulation electrodes        attached thereto, so that only those electrodes which prove most        effective for a desired purpose, e.g., pain relief, are selected        to receive a pulsed current having an amplitude, width and        repetition frequency that best meets the needs of a particular        patient.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

1. An implantable pulse generator for use with an array of electrodesimplantable within a patient so as to lie adjacent selected nervetissue, the implantable pulse generator being characterized by havingcurrent-steering capability, the implantable pulse generator comprising:a pulse generator responsive to programming signals for generatingstimulation currents; means responsive to the programming signals forselectively applying the stimulation currents to at least two electrodeswithin the array of electrodes, said at least two electrodes comprisinga first group of electrodes; and current steering means responsive todirectional signals for steering the stimulation currents from the firstgroup of electrodes to a second group of electrodes; wherein stimulationcurrents flowing between electrodes within the first group of electrodesare steered to electrodes within the second group of electrodes ascontrolled by the directional signals; wherein the current steeringmeans includes means for redistributing the stimulation currents fromthe electrodes within the first group of electrodes to the electrodeswithin the second group of electrodes in a manner that is perceived as asmooth redistribution; and wherein the redistributing means includes aformula-based algorithm means for redistributing stimulation currentfrom one of the electrodes included within the array of electrodes toanother of the electrodes included within the array of electrodes. 2.The implantable pulse generator of claim 1 wherein the formula-basedalgorithm means includes means for redistributing current amplitudesX={x₁, x₂, . . . , x_(n)} on n electrodes to a second distribution ofcurrent amplitudes Y={Y₁, y₂, . . . y_(n)} in a way that satisfies thefollowing relationship:${\sum\limits_{i = 1}^{n}\quad( {x_{i} - y_{i}} )^{2}} < {{Maximum}\quad{{{of}\quad\lbrack {\sum\limits_{i = 1}^{n}\quad( {x_{i} - y_{i}} )^{2}} \rbrack}.}}$3. The implantable pulse generator of claim 1 wherein the array ofelectrodes comprises an in-line array of electrodes located near adistal end of an implantable lead, and wherein the directional signalsare adapted to steer the stimulation currents from a group of electrodesat one location along the in-line array of electrodes to another groupof electrodes at another location along the in-line array of electrodes.4. The implantable pulse generator of claim 1 wherein the array ofelectrodes comprises in-line arrays of electrodes located near a distalend of at least two adjacent implantable leads, and wherein thedirectional signals are adapted to steer the stimulation currents from afirst group of electrodes at one location within the array of electrodesto a second group of electrodes at another location within the array ofelectrodes.
 5. The implantable pulse generator of claim 4 wherein thedirectional signals steer the stimulation current towards a second groupof electrodes that is left, right, down, up, spread down right, spreaddown left, spread up left, or spread up right relative to the firstgroup of electrodes.
 6. The implantable pulse generator of claim 1wherein the directional signals are remotely generated directionalsignals that are generated by an external programming device.
 7. Theimplantable pulse generator of claim 1 wherein the array or electrodesis adapted to be placed next to a spinal cord, and wherein thestimulation currents are steered to various locations along and near thespinal cord.
 8. The implantable pulse generator of claim 1 wherein thedirectional signals are remotely generated directional signals that aregenerated by a manually-controlled directional device.
 9. An implantablepulse generator for use with an array of electrodes implantable within apatient so as to lie adjacent selected nerve tissue, the implantablepulse generator being characterized by having current-steeringcapability, the implantable pulse generator comprising: a pulsegenerator responsive to programming signals for generating stimulationcurrents; means responsive to the programming signals for selectivelyapplying the stimulation currents to at least two electrodes within thearray of electrodes, said at least two electrodes comprising a firstgroup of electrodes; and current steering means responsive todirectional signals for steering the stimulation currents from the firstgroup of electrodes to a second group of electrodes; wherein stimulationcurrents flowing between electrodes within the first group of electrodesare steered to electrodes within the second group of electrodes ascontrolled by the directional signals; wherein the directional signalsare remotely generated directional signals that are generated by amanually-controlled directional device.
 10. The implantable pulsegenerator of claim 9 wherein the current steering means includes meansfor redistributing the stimulation currents from the electrodes withinthe first group of electrodes to the electrodes within the second groupof electrodes in a manner that is perceived as a smooth redistribution.11. The implantable pulse generator of claim 10 wherein theredistributing means includes table-based algorithm means forredistributing current from one of the electrodes included within thearray of electrodes to another of the electrodes included within thearray of electrodes.
 12. The implantable pulse generator of claim 11wherein the table-based algorithm means includes means forredistributing stimulation current from one implantable electrode toanother in small step sizes while maintaining intensity perceptionrelatively constant.
 13. The implantable pulse generator of claim 9wherein the array of electrodes comprises an in-line array of electrodeslocated near a distal end of an implantable lead, and wherein thedirectional signals are adapted to steer the stimulation currents from agroup of electrodes at one location along the in-line array ofelectrodes to another group of electrodes at another location along thein-line array of electrodes.
 14. The implantable pulse generator ofclaim 9 wherein the array of electrodes comprises in-line arrays ofelectrodes located near a distal end of at least two adjacentimplantable leads, and wherein the directional signals are adapted tosteer the stimulation currents from a first group of electrodes at onelocation within the array of electrodes to a second group of electrodesat another location within the array of electrodes.
 15. The implantablepulse generator of claim 14 wherein the directional signals steer thestimulation current towards a second group of electrodes that is left,right, down, up, spread down right, spread down left, spread up left, orspread up right relative to the first group of electrodes.
 16. Animplantable pulse generator having a multiplicity of output channels towhich a stimulating electrode may be selectively connected, comprising:a pulse generator responsive to programming signals for generatingstimulation currents, means responsive to the programming signals forselectively applying the stimulation currents to a first group of outputchannels, said first group of output channels comprising at least twooutput channels that are selectively connected to a first group ofelectrodes; and current steering means responsive to directional signalsfor steering the stimulation currents from the first group of outputchannels to a second group of output channels, said second group ofoutput channels being selectively connected to a second group ofelectrodes; wherein stimulation currents provided through the firstgroup of output channels are steered to the second group of outputchannels; wherein the current steering means includes a formula-basedalgorithm means for redistributing stimulation current from one of theoutput channels to another of the output channels.
 17. The implantablepulse generator of claim 16 wherein the formula-based algorithm meansincludes means for redistributing stimulation current amplitudes X={x₁,x₂, . . . , x_(n)} through n output channels to a second distribution ofstimulation current amplitudes Y={y₁, y₂, . . . , y_(n)} in a way thatsatisfies the following relationship:${\sum\limits_{i = 1}^{n}\quad( {x_{i} - y_{i}} )^{2}} < {{Maximum}\quad{{{of}\quad\lbrack {\sum\limits_{i = 1}^{n}\quad( {x_{i} - y_{i}} )^{2}} \rbrack}.}}$18. The implantable pulse generator of claim 16 wherein the directionalsignals are remotely generated directional signals that are generated bya manually-controlled directional device.
 19. The implantable pulsegenerator of claim 16 wherein the directional signals are remotelygenerated directional signals that are generated by an externalprogramming device.
 20. The implantable pulse generator of claim 16wherein the current steering means includes means for redistributing thestimulation currents from the first group of output channels to thesecond group of output channels in a manner that is perceived as asmooth redistribution.